File:BIF (jaspilite Meta-BIF, Paleoproterozoic Minas Gerais.jpg
Banded iron formations, or BIFs, are extinct, marine sedimentary rocks (most have been well metamorphosed) that usually consist of alternating reddish- and silvery-gray iron-rich layers. They are most common in the Paleoproterozoic rock record (2.5 to 1.6 Ga). They represent a time when Earth’s oceans “rusted out” as small amounts of atmospheric free oxygen (O2 gas) combined with dissolved iron in seawater to precipitate as iron oxide minerals. Some workers hypothesize that bacterial mats on the seafloor mediated the precipitation of iron oxides.
Many specific varities of BIFs exist, including jaspilite, taconite, quartzite-specularites, magnetitites, etc.Licensing
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/14627321977. It was reviewed on 3 August 2014 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |